Quorum sensing (QS) is a process by which bacteria assess their population density through a language of low molecular weight signalling molecules (autoinducers). Gram-negative bacteria commonly use N-acylated homoserine lactones (AHLs) as their primary autoinducers and their respective receptors (R proteins) for QS. Assessing population density allows for the modulation of gene expression levels required for group behaviour. Genes regulated by QS in Pseudomonas aeruginosa include virulence factor production and biofilm production. [Geske, G. D.; O'Neill, J. C.; Miller, D. M.; Mattmann, M. E.; Blackwell, H. E., Modulation of Bacterial Quorum Sensing: Systematic Evaluation of N-Acylated Homoserine Lactones in Multiple Species and New Insights into Their Mechanism of Action. J. Am. Chem. Soc. 2007, 129, 13613-13625.]
At high cell densities, bacteria use this chemical signaling process to switch from a nomadic existence to that of multicellular community. This lifestyle switch is significant, as numerous pathogenic bacteria use quorum sensing to turn on virulence pathways and form drug-impervious communities called biofilms that are the basis of myriad chronic infections. Over 80% of bacterial infections in humans involve the formation of biofilms, as exemplified in lung infections by Pseudomonas aeruginosa, which is the primary cause of morbidity in cystic fibrosis patients. The treatment of infections by pathogens that form biofilms costs over $1 billion/year in the US alone. Biofilms are dense extracellular polymeric matrices in which the bacteria embed themselves. Biofilms allow bacteria to create a microenviroment that attaches the bacteria to the host surface and which contains excreted enzymes and other factors allowing the bacteria to evade host immune responses including antibodies and cellular immune responses. Such biofilms can also exclude antibiotics. Further, biofilms can be extremely resistant to removal and disinfection. For individuals suffering from cystic fibrosis, the formation of biofilms by P. aeruginosa is eventually fatal. Other bacteria also respond to quorum sensing signals by producing biofilms. Biofilms are inherent in dental plaques, and are found on surgical instruments, food processing and agriculture equipment and water treatment and power generating machinery and equipment.
Gram-negative bacteria represent numerous relevant pathogens using quorum-sensing pathways. Besides P. aeruginosa, other quorum sensing bacteria include: Aeromonas hydrophila, A. salmonicida, Agrobacterium tumefaciens, Burkholderia cepacia, Chromobacterium violaceum, Enterobacter agglomeran, Erwinia carotovora, E. chrysanthemi, Escherichia coli, Nitrosomas europaea, Obesumbacterium proteus, Pantoea stewartii, Pseudomonas aureofaciens, P. syringae, Ralstonia solanacearum, Rhisobium etli, R. leguminosarum, Rhodobacter sphaeroides, Serratia liguefaciens, S. marcescens, Vibrio anguillarum, V. fischeri, V. cholerae, Xenorhabdus nematophilus, Yersinia enterocolitica, Y. pestis, Y. pseudotuberculosis, Y. medievalis, and Y. ruckeri. Studies on the above listed bacteria indicate that, while the AI is generally an AHL compound, the genes affected as well as the phenotypes resulting from induction of the promoter differ according to the particular life cycle of each bacterium. Further, quorum sensing stimulation typically results in altered expression of multiple genes.
P. aeruginosa is an opportunistic pathogen that causes severe, often fatal, infections in burn victims and cystic fibrosis patients and is therefore of direct and profound biomedical importance. P. aeruginosa uses 3-oxo-dodecanoyal homoserine lactone (OdDHL) as its autoinducer (Compound A):
While successful modifications to the acyl tail region of autoinducers have been made, modifications to the AHL head group have met limited success. Modifications to the head group are important because the lactone ring is prone to hydrolysis at pH 7 and higher. [Glansdorp, F. G.; Thomas, G. L.; Lee, J. K.; Dutton, J. M.; Salmond, G. P. C.; Welch, M.; Spring, D. R., Synthesis and stability of small molecule probes for Pseudomonas aeruginosa quorum sensing modulation. Org. Biomol. Chem. 2004, 2, 3329-3336.] This work relates to non-homoserine lactone-based autoinducer analogs for QS modulation and provides a better understanding of the structural and electronic requirements of the autoinducer's head group. Certain of the compounds of this invention are designed as autoinducer analogs for QS modulation in P. aeruginosa. 
Previous work in the field of P. aeruginosa QS modulators showed that many active non-lactone structures are highly conjugated and retain some form of the acyl chain, suggesting that a region of hydrophobicity in the acyl tail region is critical. [Muh, U.; Schuster, M.; Heim, R.; Singh, A.; Olson, E.; Greenberg, E. P., Novel Pseudomonas aeruginosa Quorum-Sensing Inhibitors Identified in an Ultra-High-Throughput Screen. Antimicrob. Agents Chemother. 2006, 50, 3674-3679; Muh, U.; Hare, B. L.; Duerkop, B. A.; Schuster, M.; Hanzelka, B. L.; Heim, R.; Olson, E. R.; Greenberg, E. P., A Structurally Unrelated Mimic of a Pseudomonas aeruginosa acyl-homoserine lactone quorum sensing signal. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 16948-16952; Lee, L. Y. W.; Hupfield, T.; Nicholson, R. L.; Hodgkinson, J. T.; Su, X.; Thomas, G. L.; Salmond, P. C.; Welch, M.; Spring, D. R., 2-Methoxycyclopentyl analogues of a Pseudomonas aeruginosa quorum sensing modulator. Molecular BioSystems 2008, 4, 505-507; Eberhard, A.; Widrig, C. A.; MaBath, P.; Schineller, J. B., Analogs of the autoinducer of bioluminescence in Vibrio fischeri. Arch. Microbiol. 1986, 146, 35-40; Rasmussen, T. B.; Givskov, M., Quorum sensing inhibitors: a bargain of effects. Microbiology 2006, 152, 895-904; Hjelmgaard, T.; Persson, T.; Rasmussen, T. B.; Givskov, M.; Nielsen, J., Synthesis of Furanone-based natural product analogues with quorum sensing antagonist activity. Bioorg. Med. Chem. 2003, 11, 3261-3271; Smith, K. M.; Bu, Y.; Suga, H., Induction and Inhibition of Pseudomonas aeruginosa quorum sensing by synthetic autoinducer analogs. Chem. Biol. 2003, 10, 81-89; Schaefer, A. L.; Hanzelka, B. L.; Eberhard, A.; Greenberg, E. P., Quorum sensing in Vibrio fischeri: Probing autoinducer-LuxR interactions with autoinducer analogs. J. Bacteriol. 1996, 178, 2897-2901; Passador, L.; Tucker, K. D.; Guertin, K. R.; Journet, M. P.; Kende, A. S.; Iglewski, B. H., Functional analysis of the Pseudomonas aeruginosa Autoinducer PAI. J. Bacteriol. 1996, 178, 5995-6000; Smith, K. M.; Bu, Y.; Suga, H., Library Screening for Synthetic Agonists and Antagonists of a Pseudomonas aeruginosa autoinducer. Chem. Biol. 2003, 10, 563-571; Ishida, T.; Ikeda, T.; Takiguchi, N.; Kuroda, A.; Ohtake, H.; Kato, J., Inhibition of quorum sensing in Pseudomonas aeruginosa by N-acyl cyclopentylamides. Appl. Environ. Microbiol. 2007, 73, 3183-3188; Fletcher, M. P.; Diggle, S. P.; Crusz, S. A.; Chhabra, S. R.; Camara, M.; Williams, P., A dual biosensor for 2-alkyl-4-quinolone quorum sensing signal molecules. Environ. Microbiol. 2007, 9, 2683-2693; Kim, C.; Kim, J.; Park, H. Y.; Park, H. J.; Lee, J. H.; Kim, C. K.; Yoon, J., Furanone derivatives as quorum sensing antagonists of Pseudomonas aeruginosa. Appl. Microbiol. Biotechnol. 2008, 80, 37-47; Estephane, J.; Dauvergne, J.; Soulere, L.; Reverchon, S.; Queneau, Y.; Doutheau, A., N-Acyl-3-amino-5H-furanone derivatives as new inhibitors of LuxR-dependent quorum sensing: Synthesis, biological evaluation and binding mode study. Bioorg. Med. Chem. Lett. 2008, 18, 4321-4324.]
Furthermore, a close examination of the crystal structure of the N-terminal domain of LasR reveals a hydrogen bond between the 3-oxo carbonyl in the acyl tail of OdDHL and a water molecule present in the LasR binding site [Bottomley, M. J.; Muraglia, E.; Bazzo, R.; Carfi, A., Molecular insights into quorum sensing in the human pathogen Pseudomonas aeruginosa from the structure of the virulence regulator LasR bound to its autoinducer. J. Biol. Chem. 2007, 282, 13592-13600.]
Published US application US2006/0178430, published Aug. 10, 2006 and International published application WO 2008/116029, published Sep. 25, 2008 relate to quorum sensing compounds and their uses. These documents are incorporated by reference in their entirety herein for their description of the state of the art and for additional methods of synthesis, methods of testing, and methods of application of quorum sensing compounds.
Janssens, J. C. A. et al. (2007) Applied Environ. Microbiol. 73(2) 535-544 reports that certain N-acyl homoserine lactones including certain thiolactones are strong activators of SdiA, the Salmonella enterica Serovar Typhimurium LuxR homologues.
Published PCT application WO2002/052949 relates to the use of autoinducer compounds as additives to animal feeds for improving animal performance.